Re: Joysticks typical polling freq.

From: Jim Brain <brain_at_jbrain.com>
Date: Fri, 13 Dec 2019 09:40:39 -0600
Message-ID: <ec59dbff-1aca-6246-2a8e-5fbc581e56a2_at_jbrain.com>
On 12/13/2019 9:21 AM, groepaz_at_gmx.net wrote:
>
> just to make it clear: its not the paddle (obviously, its just a resistor) -
> its the SID that imposes this limit. there is a capacitor that will charge in
> series with the resistor, and the SID counts how long that takes.
>
> the 512 cycles is also true for the VIC20. on the atari 800 the period is much
> longer (~20ms), the same is true for the Amiga. On the VCS *afaik* its even
> longer than that.
>
Egad, typing on my phone is atrocious... Oh well, you got the idea.  
Groepaz is more precise, it's not the paddles itself, but the circuitry 
in the machine that takes the time. And, to add a bit more (on a real 
keyboard, this time), it does not sample for 512 cycles.  It clamps the 
POT line to ground for 256 cycles to fully discharge the external 
capacitor and then (if memory serves) allows the capacitor to charge for 
256 cycles, counting the number of cycles (of the 256) it takes to reach 
some threshold.

Folks will correct if I am imprecise again, but I do know there are two 
states (the discharge state, the occurs for 256 cycles) and the sample 
state (which also takes 256 cycles).

Jim

-- 
Jim Brain
brain_at_jbrain.com
www.jbrain.com
Received on 2020-05-29 23:55:11

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